C4 3spd auto with 4.56 and 37s?

[winston vizsla]

Well I was debating 4.11 or 4.56 a while back and was convinced to get 4.56 gears with my 35x15 tsls. I haven't finished putting everything back together yet but recently drove a friends bronco with a 3spd manual, 4.56 gears and 35s and it seemed like it was geared wayyyyyyy too low. The rpms in 3rd gear going 32-36 mph sounded like what they should going 55. Nearing project completion I want to get more streetable tires, and my debate is to step up from the originally planned 35x12.50 to 37x12.50. The main debate is that for some reason tire manufacturers think its a good idea to bump the tire price up $200 more per tire so I'm looking for justification. Anyone running 4.56/37x12.5 on a C4 auto 3spd? What do your rpms look like at 55mph? Or anyone know how big of a difference 35 vs 37 would make? Any info is appreciated.

 

[skerrybronco]

Well I was debating 4.11 or 4.56 a while back and was convinced to get 4.56 gears with my 35x15 tsls. I haven't finished putting everything back together yet but recently drove a friends bronco with a 3spd manual, 4.56 gears and 35s and it seemed like it was geared wayyyyyyy too low. The rpms in 3rd gear going 32-36 mph sounded like what they should going 55. Nearing project completion I want to get more streetable tires, and my debate is to step up from the originally planned 35x12.50 to 37x12.50. The main debate is that for some reason tire manufacturers think its a good idea to bump the tire price up $200 more per tire so I'm looking for justification. Anyone running 4.56/37x12.5 on a C4 auto 3spd? What do your rpms look like at 55mph? Or anyone know how big of a difference 35 vs 37 would make? Any info is appreciated.

I use the calculator from crawlpedia
I will be running 4.56 with 35's
also some tires are not true in size, I had some 35" baja claws that were more like 33's

 

[Quick & Dirty]

The rpms in 3rd gear going 32-36 mph sounded like what they should going 55.

I'll guess you're used to driving vehicles with overdrive. Cruising at 3000 rpm isn't a big deal, it's just that most people these days aren't accustomed to it.

 

[bronconut73]

I just drove my eb for nearly an hour at 3300 rpm. A lot different feeling than my Marauder and '13 F-150 at highway speeds.
I really want one of those modern automatics in my eb one day.
So as was stated you do get used to cruising at 3000 rpm.

 

[roundhouse]

When I bought mine it had the original 235 tires 27 or 28" I think
And 4.11 gears

My top speed was about 50

Slightly faster than my dads 29 Model A

 

[DirtDonk]

You can add about 200 rpm to your calculations for a C4 in most cases, but that still puts you below the 3000 rpm level.
And higher rpms are usually a good thing when you're talking such a tire size. You're not only dealing with the effective gear ratio, but the added weight and rolling resistance of the tires, along with more wind-resistance of the taller vehicle.
So simply matching an rpm range to the smaller tire/gear combo doesn't always end up being the "correct" thing to do.

Another absolutely key factor in this equation though, is what your engine setup is going to be. Where is your engine going to be happy when pushing a 4500 lb phone booth through the air at freeway speeds?

And last is perception. Your description of your friend's Bronco experience doesn't fly. Sounds too extreme. Either he's got lower gearing than you think, or (more likely) you're just not liking the "sound" of the engine. Did he have a tachometer to watch and has he corrected the speedo for the tire size?
If not corrected, you could have actually been going 55 when you thought you were going 35!
Even the type of exhaust makes a huge difference in perception.
Maybe you've got that all factored in, but I had to ask anyway. Happens all the time.

So make sure you have a tach, a correct speedo, and know what you're wanting in the performance department.
If your engine will support the taller gearing, maybe a 4.11 wouldn't be so bad with 37" tires. But I doubt it.
With this dilemma, you can easily see why modern vehicles, and many old EB owners too, are opting for 4 and 5 speed trannies with overdrives. Makes the decision a tiny bit easier.

Paul

 

[74strokerbronco]

you missed one donk lol MAYBE he was in low range even?

 

[OverBudgetBronco]

I'm running a C4, 35's, and 4.56 runs 3000 RPM at 60 MPH.

 

[DirtDonk]

you missed one donk lol MAYBE he was in low range even?

Rats!! You're right! Should'a caught that one.
But I was actually writing that in my sleep (or should have been), so it was flying below my radar.
That's my story anyway. And I'm sticking to it.;D

Paul

 

[winston vizsla]

Funny story.. I put my 35s on and drove for the first time today with 4.56 and love them. It was night and day to his, so I drove to his house to spin his tires and see what gears it really has. I have a J shift and I'm not familiar with his T shift so I looked up the pattern and that idiot has been driving in 4L with hubs unlocked since he bought it 2 weeks ago. Said it was in that gear when he got it and hasn't changed it.

 

[DirtDonk]

Hah! Good story. And good call stroker!
Not the first time that's happened. At least a T-shift is easy once you know it's positions and characteristics.

His Bronco should have a whole new lease on life now! On the road that is.

Paul

 

[74strokerbronco]

LMAO !! knew it! 35 mph and sounded overwound in high gear had to be low range.
cool glad we actually solved one.

 

[winston vizsla]

I kind of wish mine had the t shift now after playing with his. Seemed easy and smooth. Sometimes I spend 3-4 minutes wiggling my j shift around trying to get out of 4h to 2h.

 

[skerrybronco]

I kind of wish mine had the t shift now after playing with his. Seemed easy and smooth. Sometimes I spend 3-4 minutes wiggling my j shift around trying to get out of 4h to 2h.

go for a set of twin sticks
When I bought my truck, and I was leaving I had to pull over 3 times knowing there was no way it could be in 2h final got it…..
one of my first mods was the twin sticks
highly recommend it

 

[brandenpro]

Twin sticks. It's easy to do.

 

[Mountain Ram]

I am runnin 4.56 gears, C4 and 37" Toyos. At highway speeds, it works out OK. I would have to take note of the RPMsfor you if you want, but 70mph isn't too bad. However, even with a strong stroker motor, it lacks a little off the line. I know 4.88s would be better on the low end, but it works for me. I had a weak 5.0 with this setup on 36" TSLs and it couldn't get out of its own way.

Good luck!